The three classes of organisms in the phylum annelida include freshwater worms and earthworms (oligochaetes), marine worms (polychaetes) and leeches (hirudineans). Together, these three classes contain 12,000 known speci... More »

All organisms that are found in the chordata phylum of animals have a dorsal nerve cord at some point in their lives. The dorsal nerve cord is an embryonic feature of chordatas. There are three chordata subphylums: verte... More »

The organisms belonging to phylum Nematoda are roundworms, examples of which are ascaris, trichinella, filaria worms, hookworms and pinworms. Nematodes are part of a group of animals, known as ecdysozoans, that periodica... More »

More than 15,000 species of annelids exist, including earthworms, leeches and polychaetes, which include fireworms, clam worms, lugworms and bristleworms. Earthworms are probably the most commonly known type of annelids;... More »

All vertebrates, segmented worms, such as earthworms, and cephalopods, such as squid, have closed circulatory systems. Closed circulatory systems allow larger animals to be much more active than those with open circulato... More »

Many cephalopods (including squids and octopuses) have three hearts, while earthworms have five hearts and hagfish have four. An operation exists in which a surgeon can put an additional heart into a human that can suppl... More »

Animals that live underground include earthworms, moles, blind salamanders, groundhogs, aardvarks and ants. Some underground animals regularly come to the surface in search of food and nest materials. Others remain under... More » Science Biology Zoology